Brush DC motors and AC commutator motor structures with concentrated windings

ABSTRACT

Structures of direct current motors or ac commutator (Universal) motors which use a concentrated winding on the rotor with coils wound around the teeth. The number of commutator segments is higher than the number of rotor teeth. Several coils are wound around the same tooth. The terminals of the coils are connected to different segments of the commutator. The parallel paths of the armature winding are perfectly balanced. An equal current distribution through the parallel circuits of the armature is maintained and there is no circulation current between these parallel circuits. The problems related to commutation are reduced because the value of the coil inductances is low. The copper volume of the end-windings, the Joule losses and the axial length of the motor armature are lower than a lap or a wave winding with interlocked coils. Two kinds of structures with a concentrated winding are presented: some with rotor teeth with identical dimensions and some with rotor teeth with different dimensions.

BACKGROUND OF THE INVENTION

This invention relates to direct current motors or AC commutator(Universal) motors. More particularly, this invention relates to suchmotors which use a concentrated winding on the rotor with coils woundaround the teeth.

In conventional DC motors or AC commutator (Universal) motors, there arethree types of rotor armature windings: lap windings, wave windings andfrog-legs windings. These windings are made with simple coil elementswhich are always interlocked. With an interlocked winding, the ratiobetween the axial length of the end-windings and the axial length of thearmature magnetic circuit is relatively high as it is described by KleinU.S. Pat. No. 4,329,610, Ban et al. U.S. Pat. No. 4,197,475 and IkedaU.S. Pat. No. 4,437,028.

All these windings differ primarily by the method which is used toconnect the terminals of the simple coils to the commutator. A lapwinding is also known as a multiple winding and for this kind of windingthe number of parallel paths are equal to the number of poles. The wavewinding is sometimes called a series winding and it has only two pathsin parallel, regardless of the number of poles. The frog-leg winding isthe association of a lap winding and a wave winding placed on the samearmature, in the same slots, and connected to the same commutator bars.

The most significant problem with using a lap winding is that thevoltages induced in the different parallel paths are unequal. Thesedifferences of induced voltages are due to unequal magnetic circuitreluctances or unequal fluxes under the different poles, which arecreated by rotor eccentricity, misalignment of the poles, and/ordifferences in permanent magnet magnetization. Because of the imbalancein induced voltages, circulating currents appear in the windings andthrough the brushes. These circulating currents cause unnecessaryheating of the coils and brushes and tend to produce poor commutation.

The use of equalizer connections is the common solution to overcome theundesirable effects of circulating currents. These connections improvethe current commutation and relieve the brushes of existing circulatingcurrents by providing low resistance paths which by-pass the brushcontacts. In a wave winding, the problem of the circulating currents dueto the unbalanced voltages of the parallel paths is minimized but it isalso impossible to get perfectly balanced voltages.

To avoid the interlocking of the coils, it is possible to directly windthe armature simple coils around each tooth of the rotor magneticcircuit. This kind of winding is called a concentrated winding, asdescribed in our scientific papers, “Permanent Magnet Brushless DC Motorwith Soft Metal Powder for Automotive Applications,” IEEE IndustryApplications Society, St. Louis, October 1998, and “Synthesis of HighPerformance PM Motors with Concentrated Windings,” IEEE IEMDC, Seattle,May 1999. This kind of winding is also called a non-superposed winding,as described by Ban et al. U.S. Pat. No. 4,197,475. This kind of windingreduces the copper volume of the end-winding, the copper losses and thetotal axial length of the motor. The efficiency is improved whencompared to the efficiency of classical structures. This windingstructure is also easier to realize than a lap winding or a wavewinding. When the axial length of the motor is small and the outsidediameter of the motor is important, the use of such a winding structureallows a gain of 70% as compared to the volume of copper used in anoverlapped winding.

Rotor structures with a concentrated winding have a small number ofslots and the magnetic circuit is easier to realize. The magneticcircuit can be realized with a conventional soft magnetic laminatedmaterial (a yoke made of a stack of laminations) but it is also possibleto use a soft magnetic composite material made of metal powder. Thepermeability of the soft magnetic composite is usually three times lowerthan the permeability of the conventional laminated materials like it isdescribed by Jack et al. W.O. Pat No. 99,50949. This low value ofpermeability reduces the value of the coil inductances in the armatureand the commutation process in both collector and armature is improved.A rotor structure with a small number of slots is also very well adaptedto the realization of the armature magnetic circuit of direct currentmotors or ac commutator (Universal) motors with a soft magneticcomposite material made of metal powder. With a small number of slotshaving relatively large dimension, the mechanical constraints on thedirect molding process of the rotor yoke are reduced. It is alsopossible to easily insert the end-windings in the active part of therotor magnetic circuit. This axial insertion of the end-windingsimproves the reduction of the volume of copper and the total axiallength of the motor.

However, the concentrated winding technique is too often associated andrestricted to windings with a short pitch, i.e. windings with lowerperformances than the performances of the classical winding structures.The concentrated windings with a short pitch are then limited tosub-fractional power applications (lower than 100 W) such as used inelectrical motors for computer peripherals or toys. This is the case forthe simplest and low cost brush direct current motor, which is widelyused for toys. This 2-pole motor uses permanent magnets on the statorcore, and has three teeth on its rotor core and a concentrated windingwith one coil only wound around each tooth. The armature coil terminalsare connected to a commutator with three segments and two brushes, asdescribed by Fujisaki et al. U.S. Pat. No. 4,868,433. This structure hasa winding with a short pitch of 120 electrical degrees. The windingcoefficient or the ratio between the fundamental component of magneticflux embraced by the winding and the total magnetic flux per pole isonly equal to 0.866.

The main drawbacks of this motor structure are its low performance interms of torque to weight ratio, torque ripple, and poor commutationperformance if the power is increased. With this structure, the inducedvoltages in the coil paths between brushes are not always balanced. Thisunbalanced condition of operation produce supplementary losses, torqueripples, mechanical vibrations and commutation problems. These problemsare acceptable for low power applications only.

SUMMARY OF THE INVENTION

This invention is an armature winding of a DC or AC commutator motor,which eliminates the problem of the interlocking of the coils and theproblem of circulating currents. All the path voltages are perfectlybalanced and the current commutation is improved when compared to theclassical structures.

In this invention, the number of commutator segments is higher than thenumber of rotor teeth, and a plurality of simple coils are wound aroundthe same tooth. The leads of each coil are connected to differentsegments of the commutator. Use of the present invention reduces thenumber of turns per coil for a same value of the DC voltage supply and asame speed range of the motor. The parallel paths of the armaturewinding can be perfectly balanced. An equal current distribution throughthe parallel circuits of the armature is maintained and there is nocirculation current between these parallel circuits. The inductancevalue of each simple coil is reduced and consequently the commutationproblems are minimized when compared to the case of a concentratedwinding with only one coil wound around each tooth. The copper volume ofthe end-windings, the Joule losses and the axial length of the motorarmature are lower than in the case of a lap or a wave winding withinterlocking coils. It is also possible to arrange connections of theleads of each coil to the commutator segments to obtain balanced emf inthe different coil paths between brushes. These structures can be usedefficiently for motors over a wide range of power, and their cost ofrealization is lower than the cost of classical structures.

In accordance to this invention, two kinds of structures are presented:structures with a regular distribution of rotor teeth with identicaldimensions, and structures with a regular distribution of rotor teethwith different dimensions. Both structures are efficient in terms ofperformance and cost of realization. The values of the windingcoefficients of these structures (i.e. the ratio between the fundamentalcomponent of magnetic flux embraced by the winding and the totalmagnetic flux per pole) are high.

The performance of the structures proposed in accordance with thepresent invention is similar to the performance of the classicalstructures in terms of current commutation. But the performance of thestructures proposed in accordance with the present invention in terms oftorque to winding volume ratio is higher than the performance of theclassical structures. With the proposed structures, the volume of copperis reduced, the Joules losses (copper losses) and the weight areminimized. The total axial length of the motor is reduced. Theefficiency is improved and is higher than in the case of classicalstructures. The structures of the winding and the magnetic circuit,which are proposed in accordance with the present invention, are alsoeasier to realize. The total cost of the motor is then minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an example of a direct current motorwith a concentrated winding and permanent magnets in accordance with thepresent invention.

FIG. 2 is a diagram of a developed surface of a drum armature, made byunrolling the periphery of the armature and commutator into a plane.

FIG. 3 is a diagram of construction of a machine equivalent to themachine of FIG. 2 with a rotor winding made of concentrated windingswound around the teeth.

FIG. 4 is a developed diagram of a machine with 3 rotor slots, 2 statorpoles, 6 commutator segments and 2 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 5 is a developed diagram of a machine with 6 rotor slots, 4 statorpoles, 12 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 6 is a developed diagram of a machine with 6 rotor slots, 4 statorpoles, 12 commutator segments and 2 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 7 is a diagram of a machine with 20 rotor slots, 4 stator poles, 20commutator segments, 4 brushes with a simplex lap winding and a shortpitch from 1 to 5.

FIG. 8 is a diagram of construction of a machine equivalent to themachine of FIG. 7 with a rotor winding made of concentrated windingswound around the teeth.

FIG. 9 is the diagram of a machine with 5 rotor slots, 4 stator poles,20 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 10 is a diagram of the parallel coils paths of the machinespresented in FIG. 7 and FIG. 9.

FIG. 11 is a developed diagram of a machine with 5 rotor slots, 4 statorpoles, 20 commutator segments and 2 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 12 is a developed diagram of a machine with 5 rotor slots, 4 statorpoles, 40 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 13 is a developed diagram of a machine with S rotor slots, 4 statorpoles, 40 commutator segments and 2 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 14 is a developed diagram of a machine with 10 rotor slots, 8stator poles, 40 commutator segments and 8 brushes with a rotor windingmade of concentrated windings wound around the teeth.

FIG. 15 is a developed diagram of a machine with 12 rotor slots, 4stator poles, 12 commutator segments, 4 brushes with a simplex lapwinding and a diametral pitch.

FIG. 16 is a diagram of construction of an equivalent machine of FIG. 15with a rotor winding made of concentrated windings wound around theteeth.

FIG. 17 is a developed diagram of a machine with 6 rotor slots, 4 statorpoles, 12 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around the teeth.

FIG. 18 is a developed diagram of a machine with 6 rotor slots, 4 statorpoles, 12 commutator segments, 2 brushes with a rotor winding made ofconcentrated windings and a regular distribution of rotor teeth with twodifferent dimensions.

FIG. 19 is a developed diagram of a machine with 10 rotor slots, 8stator poles, 40 commutator segments, 4 brushes with a rotor windingmade of concentrated windings and a regular distribution of rotor teethwith two different dimensions.

FIG. 20 is the axial sectional view of a permanent magnet motor with arotor magnetic circuit realized with a laminated steel material.

FIG. 21 is the axial sectional view of a permanent magnet motor with arotor magnetic circuit realized with an isotropic soft magneticcomposite material.

FIG. 22 is the axial sectional view of a motor with a rotor magneticcircuit realized with an isotropic soft magnetic composite material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment of the present invention, the rotor has a regulardistribution of rotor teeth with identical dimensions, and there are 2Ppoles, magnetized alternatively North and South in the stator. Thesepoles can be constructed with segments of permanent magnet mounted onthe surface of a core made of soft magnetic material or with coils woundaround teeth made of soft magnetic material and fed by a DC or ACcurrent. The rotor core has S slots. The simple coils of the rotor arewound around S teeth or in some case around S/2 teeth only. There are Zsegments on the commutator which are connected to the terminals of thecoils. 2B brushes are sliding on the commutator surface when the rotoris rotating. The characteristics of these machines respect the followingconditions: P is an integer and    0 < P < 10 S = 2P + A    A is aninteger equal to  −1 or 1 or 2 or S > 2 Z = k*LCM(S, 2P) ± n k is aninteger greater than 0 LCM is the Least Common Multiple of S and 2P n isequal to 0 or k B = P or less

Table 1 hereto presents some structures which respect these conditionswith k equal to 1 and n equal to 0. The number of coils per path isequal to mph (mph=Z/2P). The number of brushes 2B is normally equal tothe number of stator poles 2P. Several concentric coils are wound aroundeach rotor tooth and are connected on different commutator segments. Inthis case, the number N of concentric coils per tooth is equal to:N=Z/S

With this winding configuration, a reduction of the number of turns persimple coil is obtained. The same reduction of the number of turns isusually obtained in a classical machine structure with the same numberof stator poles by employing a higher number of rotor slots. Because theinductance value of each simple coil is reduced, commutation problemsare minimized.

It is also possible to arrange the connections of each coil to thecommutator segments to obtain balanced emf's in the different coil pathsbetween brushes. Such structures can have a value of winding coefficientKb (ratio between the fundamental component of magnetic flux embraced bythe winding and the total magnetic flux per pole) near to 1 (table 1)and consequently a high torque-weight ratio. All these machines can beused efficiently for motors and generators over a wide range of powerand for high levels of armature current. TABLE 1 2P 2 4 4 6 6 6 8 8 8 1012 S 3 5 6 5 7 8 7 9 10 12 15 Z = LCM(S, 2) 6 20 12 30 42 24 56 72 40 6060 Mph = Z/2P 3 5 3 5 7 4 7 9 5 6 5 2B 2 4 4 6 6 6 8 8 8 10 12 N 2 4 2 66 3 8 8 4 5 4 Kb 0.866 0.951 0.866 0.951 0.975 0.924 0.975 0.984 0.9510.965 0.951

It is additionally possible to reduce the number of brushes 2B and alsothe number N of concentric coils which are wound around the same rotortooth to minimize the cost of the motor. Motors having such a structureare presented in table 2. The structures listed in column 2 to 11 oftable 1 present this characteristic. It is then necessary to add someequalizer connections on the commutator segments (wires which directlyconnect segments without lying in the slots, see for example wireconecting segment 3 to 9 in FIG. 6). It should be noted that thismodification decreases the performance of the commutation process, whileincreasing the level of current in the remaining brushes. This kind ofmodification is preferably utilized in sub-fractional and fractionalpower machines. TABLE 2 2P 2 4 4 6 6 6 8 8 8 10 S 3 5 6 5 7 8 7 9 10 12Z = LCM(S, 2P) 6 20 12 30 42 24 56 72 40 60 mph = Z/2P 3 5 3 5 7 4 7 9 56 2B 2 2 2 2 2 2 2 or 4 2 or 4 2 2 N 2 2, 4 1, 2 2, 6 2, 6 1, 3 2, 2, 2,4 1, 5 4, 8, 4, 8, Kb 0.866 0.951 0.866 0.951 0.975 0.924 0.975 0.9840.951 0.965

It is also possible to reduce the number of commutator segments Z by twoand to apply the following relations to determine the number ofsegments:Z=LCM(S, 2P)/2 and Z/2P>3

With this reduction of the number of segments, as in the structurespresented in table 3, one obtains an unbalanced emf in the differentcoil paths between brushes, with the level of this unbalance beinginversely proportional to the number of coils in each parallel path.TABLE 3 2P 4 6 6 8 8 8 10 12 12 S 5 5 7 7 9 10 11 11 15 Z = LCM(S, 2P)/210 15 21 28 36 20 55 66 30 2 mph = Z/2P 5 5 7 7 9 5 11 11 5 2B 4 6 6 8 88 10 12 12 N 2 3 3 4 4 2 5 6 2 Kb 0.951 0.951 0.975 0.975 0.984 0.9510.990 0.990 0.951

In a second embodiment of the present invention, the rotor of thesestructures presents a regular distribution of rotor teeth with differentdimensions.

In particular, the stator of these machines have 2P poles magnetizedalternatively North and South. These poles can be realized withpermanent magnet segments mounted on the surface of a core made of softmagnetic material, or with coils wound around teeth made of softmagnetic material and fed by a DC or AC current. The rotor core has Sslots and rotor teeth of two different geometrical dimensions, whichalternate around the circumference of the core. The rotor coils arewound around S/2 teeth. There are Z segments on the commutator which areconnected to the terminals of the coils. 2B brushes slide on thecommutator surface when the rotor is rotating. The characteristics ofthese machines respect the following conditions: P is an integer and  1< P < 10 S = 2P + 2A   A is an integer and   1 < A < P Z = k*LCM(S/2,2P) ± n k is an integer greater than 0 LCM is the least Common 1Multiple of S/2 and 2P n is equal to 0 or k B = P or less

Table 4 herein provides exemplary structures which respect theseconditions, with k equal to 1 and n equal to 0. The number of coils perpath is equal to mph (mph=Z/2P). The number of brushes 2B is normallyequal to the number of stator poles 2P. Several concentric coils arewound around each rotor tooth and are connected on different commutatorsegments. In this case, the number N of concentric coils wound aroundeach rotor tooth is equal to: TABLE 4 N = 2Z/S 2P 4 6 6 8 8 8 10 10 1010 S 6 8 10 10 12 14 12 14 16 18 Z = LCM(S/2, 2P) 12 12 30 40 24 56 6070 40 90 mph = Z/2P 3 4 5 5 3 7 3 7 4 9 2B 4 6 6 8 8 8 10 10 10 10 N 4 36 8 4 8 10 10 5 10 Kb 1 1 1 1 1 1 1 1 1 1

These motor structures offer the same advantages of the previous oneslisted in table 1 in terms of current commutation performance andbalanced parallel coils path. But it is also possible to get a higherwinding coefficient Kb (equal to unity, Kb=1), and to maximize thetorque per unit of volume of copper. These structures can be usedefficiently for motors and generators over a wide power range and forhigh levels of armature current. It is also possible, as in the case ofthe previous structures of table 1, to apply different simplificationsfor the choice of the number of brushes, the number commutator segmentsand the number of concentric coils per tooth to reduce the cost of themotor and simplify the realization.

It must be noticed that all the proposed solutions which are inaccordance with the present invention can be used with different brushwidths.

According to the present invention, a DC or AC commutator motor can bemanufactured with a magnetic circuit made of laminated steel or made ofa soft magnetic composite material.

In particular, when an isotropic soft magnetic composite is used, aportion of the magnetic flux can also circulate in the axial direction.For this reason, it is possible to expand the tooth tips in the axialdirection, and thus maximize the axial length of the active air-gap areafor a given total axial length of the motor as fixed by thespecifications of the application. In such structures, the air-gap fluxis concentrated into the center part of the rotor teeth under the coilsand the yoke. Because the axial length of the center part of the rotorteeth under the coils and the axial length of the yoke is smaller thanthe axial length of the tooth tips, the end-windings, the commutator andthe brushes are now axially inserted and the total axial length of themotor is reduced. With this method, the isotropic properties of the softmagnetic composites are used to minimize the axial length of a motorwithout reducing the torque performance.

When an isotropic soft magnetic composite is used, the cross-sectionprofile of the center part of the rotor and stator teeth under the coilscan be made round, oval, or circular. These profiles can reduce the riskof destruction of the insulation by a sharp bending of the windingcoils, and maximize the copper filling factor.

It is also possible to skew the permanent magnets or the teeth of thestator to reduce the variations of the air-gap reluctance or the coggingtorque. The same result can be obtained by skewing the teeth of therotor. When an isotropic soft magnetic composite is used, it is possibleto skew only the tooth tips.

FIG. 1 shows a cross-sectional view of an example of a direct currentmotor with a concentrated winding and permanent magnets in accordancewith the present invention. Part 1 is the yoke of the stator. Part 2 isone of the stator poles, which are magnetized alternatively North andSouth, and which is made of a segment of permanent magnet. Part 3 is thetip of a rotor tooth. Part 4 is the center part of the rotor tooth underthe coils. Part 5 is the yoke of the rotor. Part 6 is the concentratedwinding, wound around a stator tooth. Part 7 is one of the segments orbars of the commutator. Part 8 is one of the brushes in contact with thesegments of the commutator and which is used to feed the supply currentto the armature winding.

FIGS. 2, 3 and 4 each illustrates a method to derive the structure of amachine with a rotor winding made of concentrated windings wound aroundthe teeth from the structure of a classical machine. Each of thesestructures presents the same number of stator poles, and a commutatorsegment number equal to the rotor slot number.

More particularly, FIG. 2 shows a classical structure with 6 rotorslots, 2 stator poles, 6 segments on the commutator and 2 brushes. Thewinding of the rotor is a simplex lap winding, overlapped with a shortpitch of 120 electric degrees. The connections of the terminals of eachsimple coil to the segments of the commutator are arranged to get coilspaths perfectly balanced in the armature winding.

In FIG. 2, the 6 simple coils of the armature winding are denoted 1.1,1.2, 2.1,2.2,3.1,3.2. Coils 1.1 and 1.2 denote simple coils which havethe same phase of emf, because their positions relative to the statorpoles are identical. The same is the case with coils 2.1, 2.2, and withcoils 3.1, 3.2. The dots in FIG. 2 are polarity marks and indicate thepolarity of the winding, in accordance with standard notation in theart. The teeth defining the 6 rotor slots are defined by T1 through T6,respectively. The commutator segments are labeled 1 through 6respectively, and as can be seen, a voltage V is applied to the brushesB1, B2. The north and south stator poles are labeled N and S,respectively. Similar nomenclature is used in the balance of thefigures.

In comparison with FIG. 2, by regrouping simple coils which have thesame phase of emf on the same tooth of the rotor, one avoids theinterlocking of the end-windings, as is shown on FIG. 3. Moreparticularly, FIG. 3 is a diagram of construction of a machineequivalent to the machine of FIG. 2 in terms of torque and emfcharacteristics, magnetic flux and current density, where the rotorwinding in FIG. 3 is made of concentrated windings around the teeth. Thesimple coils having emf's which are in phase as coils 1.1 and 1.2 inFIG. 2 are regrouped on a same tooth. To increase the size of the slotsfilled with conductors and to preserve the same total copper section ofthe whole rotor armature in the original machine of FIG. 2 and in theequivalent machine of FIG. 3 (i.e. the sum of the copper section of eachslot), the teeth around the empty slots are regrouped to form the newdistribution of teeth presented in FIG. 3. As compared to FIG. 2, theposition of the tooth tips in FIG. 3 are not modified at the level ofthe airgap; however the center parts of the teeth of the machine of FIG.2 between the tooth tips and the inner rotor yoke have been shifted inFIG. 3 to form a single big tooth. With this method, the pattern of theno-load magnetic flux spatial distribution in the airgap is not modifiedand the total section of the soft magnetic material in the teeth fromthe original machine of FIG. 2 to the equivalent machine of FIG. 3 isalso preserved to avoid a saturation of the magnetic flux. Therefore thetotal amounts of soft magnetic material in the yoke and copper in theslots are modified as well. One gets a machine with a concentratedwinding presented in FIG. 3 which is equivalent to the initial machineof FIG. 2, as explained above. The shape and the emf amplitude in eachcoil are not modified.

As shown in FIG. 3, some slots are empty and it is possible to groupteeth around each empty slot. The position of the tooth tips are notmodified at the level of the airgap, only the center parts of the teethbetween the tooth tips and the inner rotor yoke are shifted to form asingle big tooth. The pattern of the no-load magnetic flux spatialdistribution in the airgap is not modified, as is shown in FIG. 3. Onecan then concentrate the simple coils around each tooth. The totalsection of soft magnetic material in the teeth and the total coppersection of the whole rotor armature are preserved and are identical tothe corresponding sections in the initial machine with a classicalstructure.

FIG. 4 is a developed diagram of a machine with 3 rotor slots, 2 statorpoles, 6 commutator segments and 2 brushes with a rotor winding made ofconcentrated windings wound around the teeth. Two simple coils, likecoils 1.1 and 1.2, are wound around the same tooth and are connected todifferent segments of the commutator. The connections to the commutatorsegments are identical to the connections used in the machine shown inFIG. 2. One can notice on the diagram on the right that the coils pathsare not modified. Each simple coil wound around a same tooth like coil1.1 and coil 1.2 has an identical emf. The total emf's across eachparallel coil path are now perfectly balanced, even if the airgapreluctances or the magnetization of the permanent magnets under eachpole of the stator are not perfectly identical. This machine isequivalent to the machine presented in FIG. 2 in terms of torque and emfcharacteristics, magnetic flux density and current density.

The machine presented on the FIG. 4 has a concentrated winding, which isequivalent to the initial machine of FIG. 2, in terms of torque and emfcharacteristics, magnetic flux and current density. The connections ofthe terminals of the simple coils to the commutator are identical inboth machines (i.e. machines on FIG. 2 and FIG. 4). The coil paths inthe armature winding are always balanced: i.e. the total emf's acrosseach parallel coil path are balanced, even if the airgap reluctances orthe magnetization of the permanent magnets under each pole of the statorare not perfectly identical.

FIG. 5 is a developed diagram of a machine with 6 rotor slots, 4 statorpoles, 12 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around the teeth. This machine is derivedfrom the machine presented in the FIG. 4 by doubling the periodicity ofits structure.

In addition, several modifications can be realized to simplify thesestructures in the case of a sub-fractional power machine made inaccordance to the present invention. In particular, it is possible toreduce the number of brushes while adding equalizer connections on thecommutator. This is shown in FIG. 6, which is a developed diagram of amachine with 6 rotor slots, 4 stator poles, 12 commutator segments and 2brushes with a rotor winding made of concentrated windings wound aroundthe teeth. This machine is an evolution of the machine presented in FIG.5 with a reduced number of brushes and with equalizer connections addedon the commutator. It can be seen in FIG. 6 that the two coils woundaround each tooth are connected in parallel by equalizer connections.Optionally, one could reduce the number of simple coils around eachtooth to one, with several of the commutator segments not being directlyconnected to coil terminals.

The same method is applied on FIGS. 8 and 9 for another example, inaccordance to the present invention. Initially FIG. 7 depicts aclassical machine having 20 rotor slots, 4 stator poles, 20 segments onthe commutator and 4 brushes. The winding of the rotor is overlappedwith a short pitch of 1 to 5. The coil paths in the armature winding arepresented on FIG. 10.

FIG. 8 is a diagram of the construction of a machine equivalent to themachine of FIG. 7 in terms of torque and emf characteristics, magneticflux and current density, with the rotor winding in FIG. 8 made ofconcentrated windings wound around the teeth. The coils having emf'swhich are in phase as coils 1.1, 1.2, 1.3, 1.4 are regrouped on a sametooth. To increase the size of the slots filled with conductors and topreserve the same total copper section of the whole rotor armature inthe original machine of FIG. 7 and in the equivalent machine of FIG. 8(i.e. the sum of the copper section of each slot), the teeth around theempty slots are regrouped to form the new distribution of teethpresented in FIG. 8. The position of the tooth tips are not modified atthe level of the airgap, only the center parts of the teeth of themachine of FIG. 7 between the tooth tips and the inner rotor yoke havebeen shifted to form a single big tooth. With this method, the patternof the no-load magnetic flux spatial distribution in the airgap is notmodified. The total section of soft magnetic material in the teeth fromthe original machine of FIG. 7 to the equivalent machine of FIG. 8 isalso preserved to avoid saturation of the magnetic flux. Therefore thetotal amounts of soft magnetic material in the yoke and copper in theslots are not modified as well. One gets a machine with a concentratedwinding presented in FIG. 8 which is equivalent to the initial machineof FIG. 7, as explained above. The shape and the emf amplitude in eachcoil are not modified.

FIG. 9 is the diagram of a machine with 5 rotor slots, 4 stator poles,20 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around the teeth. Four simple coils arewound around a same tooth and are connected to different segments of thecommutator. Connections to the commutator segments are identical to theconnections used in the machine presented on the FIG. 7. Each simplecoil wound around a same tooth, like coils 1.1 and 1.2 and 1.3 and 1.4,has an identical emf. The total emf's across each parallel coil path(FIG. 10) are now perfectly balanced, even if the airgap reluctances orthe magnetization of the permanent magnets under each pole of the statorare not perfectly identical. This machine is equivalent to the machinepresented in FIG. 7 in terms of torque and emf characteristics, magneticflux density and current density.

FIG. 10 is a diagram of the parallel coils paths of the machinespresented in FIG. 7 and FIG. 9.

Several modifications can be realized to simplify these structures inthe case of a sub-fractional power machine in accordance to the presentinvention. It is possible to reduce the number of brushes while addingequalizer connections on the commutator. One can also reduce the numberof simple coils as it is presented on the FIG. 11. In accordance to thepresent invention, FIG. 12 shows the same kind of motor as is depictedin FIG. 9 with a higher periodicity of structure.

More particularly, FIG. 11 is a developed diagram of a machine with 5rotor slots, 4 stator poles, 20 commutator segments and 2 brushes with arotor winding made of concentrated windings wound around the teeth. Thismachine is an evolution of the machine presented in the FIG. 9 with areduced number of brushes and equalizer connections are added on thecommutator. In this machine, it is also possible to reduce the number ofsimple coils on each tooth to 2 as is shown in FIG. 11.

Likewise, FIG. 12 is a developed diagram of a machine with 5 rotorslots, 4 stator poles, 40 commutator segments and 4 brushes with a rotorwinding made of concentrated windings wound around the teeth. Thismachine is an evolution of the machine presented in the FIG. 9 with ahigher number of simple coils and number of commutator segments.

FIG. 13 shows the same structure of motor presented on FIG. 9 with ahigher number of commutator segments and a higher simple coil numberwound around a tooth, in accordance with the present invention.

More particularly, FIG. 13 is a developed diagram of a machine with 5rotor slots, 4 stator poles, 40 commutator segments and 2 brushes with arotor winding made of concentrated windings wound around the teeth. Thismachine is an evolution of the machine presented in the FIG. 12 with areduced number of brushes and equalizer connections added on thecommutator. The number of segments between 2 brushes of inverse polarity(+ and −) is increased according to the solution presented with respectto FIG. 9 (10 segments vs. 5 segments). Therefore, the voltage between 2successive segments is lower. This kind of solution is of utility whenthe supply voltage is high and it permits limiting the amplitude of thevoltage between 2 successive segments. It is possible to reduce thenumber of simple coils on each tooth to 2 in this figure.

FIG. 14 is an evolution of the solution presented on FIG. 9, inaccordance to the present invention, with a higher periodicity of thestructure.

More particularly, FIG. 14 is a developed diagram of a machine with 10rotor slots, 8 stator poles, 40 commutator segments and 8 brushes with arotor winding made of concentrated windings wound around the teeth. Thismachine is derived from the machine presented in the FIG. 9 by doublingthe periodicity of its structure.

The present invention is applied on FIGS. 16 and 17, which depict amachine with a rotor winding made of concentrated windings and a regulardistribution of rotor teeth with two different dimensions. The classicalmachine for reference presented in FIG. 15 has 12 rotor slots, 4 statorpoles, 12 segments on the commutator and 4 brushes. The winding of therotor is overlapped with a diametral pitch.

FIG. 16 is a diagram of construction of an equivalent machine of FIG.15, in terms of torque and emf characteristics, magnetic flux andcurrent density, with the rotor winding in FIG. 16 made of concentratedwindings wound around the teeth. The coils having emf's which are inphase as coils 1.1, 1.2, 1.3, 1.4 are regrouped on a same tooth. Toincrease the size of the slots filled with conductors and to preservethe same total copper section of the whole rotor armature in theclassical machine of FIG. 15 and in the equivalent machine of FIG. 16(i.e. the sum of the copper section of each slot), the teeth around theempty slots are regrouped to form the new distribution of teethpresented in FIG. 16. The position of the tooth tips are not modified atthe level of the airgap, only the center parts of the teeth of themachine of FIG. 15 between the tooth tips and the inner rotor yoke havebeen shifted to form a single big tooth. With this method, the patternof the no-load magnetic flux spatial distribution in the airgap is notmodified. The total section of soft magnetic material in the teeth fromthe original machine of FIG. 15 to the equivalent machine of FIG. 16 isalso preserved to avoid a saturation of the magnetic flux. Therefore thetotal amounts of soft magnetic material in the yoke and copper in theslots are not modified as well. One can notice that all the coils arewound around 3 teeth only. One gets a machine with a concentratedwinding presented in FIG. 16 which is equivalent to the initial machineof FIG. 15, as explained above. The shape and the emf amplitude in eachcoil are not modified.

FIG. 17 is a developed diagram of a machine with 6 rotor slots, 4 statorpoles, 12 commutator segments and 4 brushes with a rotor winding made ofconcentrated windings wound around 3 teeth. There is a regulardistribution of rotor teeth of two different dimensions, with teeth T1,T2 and T3 of one dimension, and teeth T4, T5 and T6 of a seconddimension. Four simple coils are wound around each tooth and areconnected to different segments of the commutator. The connections tothe commutator segments are identical to the connections used in themachine presented on the FIG. 15. The coils paths are perfectlybalanced. This machine is equivalent to the machine presented in FIG. 15in terms of torque and emf characteristics, magnetic flux density andcurrent density, with a winding coefficient equal to 1. The performanceof this kind of concentrated winding machine is high.

In the case of a sub-fractional power machine constructed in accordancewith this invention, several modifications can be made to simplify thestructure. For example, it is possible to reduce the number of brusheswhile adding equalizer connections on the commutator. FIG. 18 is adeveloped diagram of a machine with 6 rotor slots, 4 stator poles, 12commutator segments, 2 brushes with a rotor winding made of concentratedwindings and a regular distribution of rotor teeth with two differentdimensions. This machine is an evolution of the machine presented in theFIG. 17 with a reduced number of brushes and equalizer connections addedon the commutator. In this machine, it is also possible to reduce thenumber of simple coils on each tooth to 2 as is shown in FIG. 18.

FIG. 19 presents the result of another example of a machine with a rotorwinding made of concentrated windings and a regular distribution ofrotor teeth with two different dimensions. The initial machine has 40rotor slots, 8 stator poles, 40 segments on the commutator and 8brushes. The equivalent machine, in accordance to the present invention,has 10 rotor slots with rotor teeth of two different geometricaldimensions (teeth T1 through T5 being of one dimension, and T6 throughT10 being of a second dimension), 8 stator poles, 40 segments on thecommutator and 4 brushes. There are 8 simple coils per tooth.Connections of the simple coils on the commutator are the same as theinitial machine. It is possible to reduce the number of brushes whileadding equalizer connections on the commutator.

FIG. 20 is an axial sectional view of a permanent magnet motor with arotor magnetic circuit realized with a laminated steel material.Usually, the axial dimension of the magnetic circuit of the rotor (parts3, 4, 5) is lower than the axial length of the permanent magnet. Theflux of the permanent magnets is thus concentrated axially into therotor and it is possible to insert, partially, the end-winding under thepermanent magnets axial length. This modification of the axial dimensionof the rotor reduces the total axial length of the motor.

FIG. 21 is the axial sectional view of a permanent magnet motor with arotor magnetic circuit realized with an isotropic soft magneticcomposite material. In an isotropic magnetic material, a portion of themagnetic flux can also circulate in the axial direction. It is thereforepossible to increase the flux concentration without decreasing theperformance of the motor. The center part of the rotor teeth under thecoils (part 4) and the rotor yoke (part 5) have the same axial dimensionand the tips of the teeth (part 3) have an axial dimension nearlyidentical to the axial length of the permanent magnets. The total axiallength of the motor is reduced when compared to a rotor with a laminatedsteel (FIG. 20). It is then possible with this structure to maximize theaxial length of the active air-gap area for a total axial length fixedby the specifications of the application.

FIG. 22 is the axial sectional view of a motor with a rotor magneticcircuit realized with an isotropic soft magnetic composite material. Thestructure presented on FIG. 22 is an evolution of the structure of theFIG. 21. The center part of the rotor teeth under the coils (part 4) andthe rotor yoke (part 5) have the same axial dimension and the tips ofthe teeth (part 3) have an axial dimension nearly identical to the axiallength of the permanent magnets. Part 4 and part 5 are shifted axially.The end-windings, commutator and brushes are inserted partially ortotally in the axial direction for a further minimization of the totalaxial length of the motor.

The proposed motor structures of this invention are very well adapted tothe realization of the rotor magnetic circuit with a soft magneticcomposite material made of metal powder. With a small number of slotswith relatively large dimensions, the mechanical constraints on thedirect molding process of the rotor yoke are reduced. An isotropic softmagnetic composite is also well adapted to realize an axial air-gap fluxconcentration in the rotor or the stator magnetic circuit and to reducethe total axial length of the motor without decreasing the performancesof motor. The tips of the teeth can be expanded axially and used toconcentrate the magnetic flux in the airgap, axially, into the teeth andthe yoke of the rotor or the stator (FIGS. 21 & 22). The axial length ofthe tips of the rotor teeth can have an axial dimension nearly identicalto the axial length of the permanent or the axial length of the toothtips of the stator. The axial dimension of the teeth and the yoke arethe same and can be lower than the axial dimension of the tooth tips(FIGS. 21 & 22). The center part of the rotor teeth under the coils andthe rotor yoke can also be decentered and shifted axially (FIG. 22). Itis also possible to axially insert the end-windings inside the toothtips (FIGS. 21 & 22). The commutator and the brushes can also beinserted partially or totally in the axial direction under the rotortooth tips (FIG. 22). This kind of structure has utility in reducing thetotal axial length of the motor.

When an isotropic soft magnetic material is used, it is also useful tomake the cross-section profile of the center part of the rotor andstator teeth under the coils, round, oval, or circular to get areduction of the risk of destruction of the insulation by a sharpbending of the winding coils, and to maximize the copper filling factor.

All the embodiments of this invention can be used with different brushwidths. The rotor slots and/or the stator slots can be skewed to reducethe variations of the magnetic reluctance. In the case of a stator withpermanent magnets, it is also possible to skew the rotor slots and/orthe permanent magnets to reduce the cogging torque. When an isotropicsoft magnetic composite is used, it is possible to skew only the tips ofthe rotor teeth and/or the tips of the stator teeth.

The new structures of DC and AC commutator motor of the presentinvention can be used in a large variety of applications (automotiveapplications, electrodomestic appliances, corded electric tools,electric vehicles, fractional and sub-fractional DC and AC commutatormotors, etc.). The improved efficiency and the simplifications realizedon the rotor winding will provide a lower realization cost and higherperformances than classical structures.

While only some embodiments of the present invention are describedabove, it is obvious that several modifications or simplifications arepossible without departing from the spirit of the present invention.Thus, the invention may be applied to motors with a radial airgap ortranversal airgap. Also, the invention can be used in machines having aninner rotor or an outer rotor structure. It is also understood thatvarious further changes and modifications can be made without departingfrom the spirit and scope of the invention.

1-4. (canceled)
 5. A direct current motor comprising: a stator with 2Ppoles; a rotor core including a core of ferromagnetic material having Sslots and S teeth separated from the stator core by an airgap; a rotorcore having a plurality of teeth, each tooth having the same geometricaldimensions: a concentrated winding rotor with a plurality of coils ofinsulated wire being wound around each rotor tooth; a commutator with anumber of segments Z; wherein the number of stator poles 2P, the numberof rotor slots S and the number of segments on the commutator Z satisfythe following conditions: P is an integer and 0 < P < 10 S = 2P + A A isan integer equal to −1 or 1 or 2 or 3 or 4 S > 2 Z = k*LCM(S, 2P) ± n kis an integer greater than 0 LCM is the Least Common Multiple of S and2P n is equal to 0 or k or Z = LCM(S, 2P)/2 and  Z/2P > 3


6. The direct current motor of claim 5, wherein each pole comprises apermanent magnet mounted on the surface of a core of a ferromagneticmaterial.
 7. The direct current motor of claim 5, wherein each polecomprises a coil wound around a tooth made of a ferromagnetic material.8. An AC commutator (Universal) motor comprising: a stator with 2Ppoles, each comprising a coil wound around the tooth of a core of aferromagnetic material; a rotor core including a core of ferromagneticmaterial having S slots and S teeth separated from the stator core by anairgap, wherein each tooth has the same geometrical dimensions; aconcentrated winding rotor having a plurality of insulated wire coilsbeing wound around each rotor tooth; a commutator with a number ofsegments Z; wherein the number of stator poles 2P, the number of rotorslots S and the number of segments on the commutator Z satisfy thefollowing conditions: P is an integer and 0 < P < 10 S = 2P + A A is aninteger equal to −1 or 1 or 2 or 3 or 4 S > 2 Z = k*LCM(S, 2P) ± n k isan integer greater than 0 LCM is the Least Common Multiple of S and 2P nis equal to 0 or k or Z = LCM(S, 2P)/2 and  Z/2P > 3


9. A direct current motor comprising: a stator with 2P poles; a rotorcore including a core of ferromagnetic material having S lots and Steeth separated from the stator core by an airgap; wherein S/2 of theteeth have different geometrical dimensions from the remaining teeth; aconcentrated winding rotor having a plurality of coils of insulated wirebeing wound around S/2 of the rotor teeth; a commutator with a number ofsegments Z; wherein the number of stator notes 2P, the number of rotorslots S and the number of segments on the commutator Z to satisfy thefollowing conditions: P is an integer and 1 < P < 10 S = 2P + 2A A is aninteger and 1 < A < P Z = k*LCM(S/2, 2P) ± n  k is an integer greaterthan 0 LCM is the Least Common Multiple of S/2 and 2P n is equal to 0 ork or Z = LCM(S/2, 2P)/2


10. The direct current motor as in claim 9, wherein each pole comprisesa permanent magnet mounted on the surface of a core of a ferromagneticmaterial.
 11. The direct current motor as in claim 9, wherein each polecomprises a coil wound around a tooth made of a ferromagnetic material.12. An AC commutator (Universal) motor comprising: a stator with 2Ppoles; a rotor core including a core of ferromagnetic material having Sslots and S teeth separated from the stator core by an airgap, whereinS/2 teeth have different geometrical dimensions from the remainingteeth; a concentrated winding rotor having a plurality of coils ofinsulated wire being wound around S/2 rotor teeth; a commutator with anumber of segments Z; wherein the number of stator poles 2P, the numberof rotor slots S and the number of segments on the commutator Z tosatisfy the following conditions: P is an integer and 1 < P < 10 S =2P + 2A A is an integer and 1 < A < P Z = k*LCM(S/2, 2P) ± n k is aninteger greater than 0 LCM is the Least Common Multiple of S/2 and 2P nis equal to 0 or k or Z = LCM(S/2, 2P)/2


13. The AC commutator (Universal) motor as in claim 12, wherein eachpole comprises a permanent magnet mounted on the surface of a core of aferromagnetic material.
 14. The AC commutator (Universal) motor as inclam 12, wherein each pole comprises a coil wound around a tooth made ofa ferromagnetic material. 15-28. (canceled)